Business ProfileforPure Dental Spa

I haven't gone to the dentist in a few years so I decided I needed to rip the bandaid and go in for a cleaning and x-ray, I picked them because they appeared to have good reviews. After the x-ray they presented me with paperwork of a breakdown of the costs for 12 cavities (which to me at the time didn't sound right) and a deep cleaning, they divided it into right side of my mouth and left side of my mouth for the work. The right side was going to be $273 after insurance and the left side was going to be a bit more, closer to $650 after insurance. I signed paperwork agreeing that would be the amount I would pay and set up my appointment for the right side of my mouth. The first appointment went well, I paid $223 after the initial $50 deposit for setting the appointment date. I made the next appointment for the left side of my mouth a few days later in early July, this is when things began to get frustrating. They initially told me $650 for the left side of my mouth but when they called to confirm my appointment I asked them how much it would cost and they told me $293. I asked them why I was quoted a different amount a few days before and they told me someone had made a mistake. After the second appointment I paid $293 in full on my fsa card from my job, they asked if I wanted a receipt emailed, I said yes but it was never sent, they gave me a small piece of paper that looked like a regular store receipt after paying no invoice. A few days later my fsa said the dentist didn't give enough proof so they would not pay for it and asked me to pay the $293 out of my pocket. I asked the dentist for a detailed invoice to provide for my fsa account FIVE TIMES and each time they gave me a different paper, all with different amounts. Today I received an email that I owe them $1,888.20. I'm getting in trouble with my fsa because of the dentist and now the dentist is asking for more money too. I'm completely at a loss at this point